As the age of point-of-care healthcare has come, the importance of gene analysis, external diagnosis, gene sequencing, etc. is being emphasized. Also, demand therefor is gradually increasing. Thus, a system capable of performing a large amount of tests by using only a small amount of samples has been developed and implemented. Also, in order to realize such a system, microfluidic devices such as a microfluidics chip or a lab-on-a-chip (LOC) have attracted much attention. The microfluidic device including a plurality of micro-channels and a plurality of micro-chambers is designed to control and manipulate tiny amounts of fluids, for example, amounts from several nl to several ml. By using the microfluidic device, a reaction time of microfluidics may be minimized, and reaction of the microfluidics and measurement of a result of the reaction may be performed at the same time. Such a microfluidic device may be manufactured in various ways, and various materials may be used according to a method of manufacturing the microfluidic device.
Meanwhile, for example, during a gene analysis process, in order to ascertain whether a certain deoxyribonucleic acid (DNA) exists in a sample or to exactly ascertain an amount of DNA, a process of refining/extracting an actual sample and then sufficiently amplifying the sample to be measured is required. From among various gene amplification methods, for example, a polymerase chain reaction (PCR) is most widely used. Also, fluorescence detection is mainly used as a method of detecting DNA amplified through PCR. For example, in quantitative real-time PCR (qPCR), a plurality of fluorescent dyes/probes and primer sets are used to amplify a target sample and to detect/measure the target sample in real time. For example, regarding the qPCR using a Taqman probe, the qPCR uses the Taqman probe that has fluorescence properties when separated from a template during amplification of DNA. In other words, as a PCR cycle progresses, a number of the Taqman probes separated from the templates exponentially increases, and thus a fluorescence signal level exponentially increases. Changes in the fluorescence signal level are measured by using an optical system to enable determination of presence of a target sample or quantitative analysis. As the PCR cycle progresses, a curve of a fluorescence signal level follows an S-curve, and a Ct (threshold cycle) value is set at a point where the fluorescence signal level sharply changes and the Ct value is measured. A platform, such as external diagnosis, gene analysis, development of a biomarker, or gene sequencing, to which a qPCR technology is applied, has already been commercialized.
In detecting a fluorescence signal by using a bio-reaction, such as a PCR, occurring in a microfluidic device using tiny amounts of fluid, e.g., from several nl to several ml, a signal level is generally proportional to an amount of sample solutions, and a detectable limitation is referred to as limit of detection (LOD). An amplifier may be used to raise a signal level, but in this case, noise is also amplified. Accordingly, an amplifier is not proper to detect a tiny amount of targets. Therefore, research on a method of improving LOD by minimizing a loss of a fluorescence signal is required.